An organic electroluminescence (“electroluminescence” will be referred to as “EL”, hereinafter) device is a spontaneous light emitting device which utilizes the principle that a fluorescent substance emits light by energy of recombination of holes injected from an anode and electrons injected from a cathode when an electric field is applied. Since an organic EL device of the laminate type driven under a low electric voltage was reported by C. W. Tang of Eastman Kodak Company (C. W. Tang and S. A. Vanslyke, Applied Physics Letters, Volume 51, Pages 913, 1987), many studies have been conducted on organic EL devices using organic materials as the constituting materials. Tang et al. used a laminate structure using tris(8-hydroxyquinolinolato)aluminum for the light emitting layer and a triphenyldiamine derivative for the hole transporting layer. Advantages of the laminate structure are that the efficiency of hole injection into the light emitting layer can be increased, that the efficiency of forming excitons which are formed by blocking and recombining electrons injected from the cathode can be increased, and that excitons formed within the light emitting layer can be enclosed. As the structure of the organic EL device, a two-layered structure having a hole transporting (injecting) layer and an electron transporting and light emitting layer and a three-layered structure having a hole transporting (injecting) layer, a light emitting layer and an electron transporting (injecting) layer are well known. To increase the efficiency of recombination of injected holes and electrons in the devices of the laminate type, the structure of the device and the process for forming the device have been studied.
As the light emitting material of the organic EL device, chelate complexes such as tris(8-quinolinolato)aluminum complex, coumarine derivatives, tetraphenylbutadiene derivatives, bisstyrylarylene derivatives and oxadiazole derivatives are known. It is reported that light in the visible region ranging from blue light to red light can be obtained by using these light emitting materials, and development of a device exhibiting color images is expected (for example, Patent Reference 1, Patent Reference 2 and Patent Reference 3).
A device using a phenylanthracene derivative as the light emitting material is disclosed in Patent Reference 4. A material in which naphthyl groups are bonded at the 9- and 10-positions of anthracene is disclosed in Patent Reference 5. These anthracene derivatives are used as the material emitting blue light. However, an improvement in the life of the device has been required.
A material in which fluoranthene groups are bonded at the 9- and 10-positions of anthracene is disclosed in Patent Reference 6. This anthracene derivative is used as the material emitting blue light. However, an improvement in the life of the device has been required.
It is disclosed in Patent Reference 7 that various anthracene derivatives are used as the hole transporting material. However, the evaluation of these compounds as the light emitting material has not been made.
It is disclosed in Patent Reference 8 that devices using asymmetric anthracene derivatives as the material emitting blue light exhibit great efficiencies of light emission and have long lives. Although the asymmetric anthracene derivatives are excellent materials emitting blue light, some of the derivatives have a drawback in that the glass transition temperature (Tg) is rather low, and an improvement in Tg has been desired.
[Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei 8(1996)-239655
[Patent Reference 2] Japanese Patent Application Laid-Open No. Heisei 7(1995)-138561
[Patent Reference 2] Japanese Patent Application Laid-Open No. Heisei 3(1991)-200889
[Patent Reference 4] Japanese Patent Application Laid-Open No. Heisei 8(1996)-12600
[Patent Reference 5] Japanese Patent Application Laid-Open No. Heisei 11(1999)-3782
[Patent Reference 6] Japanese Patent Application Laid-Open No. 2001-257074
[Patent Reference 7] Japanese Patent Application Laid-Open No. 2000-182776
[Patent Reference 8] WO 2004-18587